THE DESIGN OF SAMPLING TRANSECTS FOR CHARACTERIZING WATER-QUALITY IN ESTUARIES

Citation
Ad. Jassby et al., THE DESIGN OF SAMPLING TRANSECTS FOR CHARACTERIZING WATER-QUALITY IN ESTUARIES, Estuarine, coastal and shelf science, 45(3), 1997, pp. 285-302
Citations number
45
Categorie Soggetti
Oceanografhy,"Marine & Freshwater Biology
ISSN journal
02727714
Volume
45
Issue
3
Year of publication
1997
Pages
285 - 302
Database
ISI
SICI code
0272-7714(1997)45:3<285:TDOSTF>2.0.ZU;2-M
Abstract
The high spatial variability of estuaries poses a challenge for charac terizing estuarine water quality. This problem was examined by conduct ing monthly high-resolution transects for several water quality variab les (chlorophyll a, suspended particulate matter and salinity) in San Francisco Bay (California, U.S.A.). Using these data, six different wa ys of choosing station locations along a transect, in order to estimat e mean conditio:ns, were compared. In addition, Il approaches to estim ating the variance of the transect mean when stations are equally spac ed were compared, and the relationship between variance of the estimat ed transect mean and number of stations was determined. The results pr ovide guidelines for sampling along the axis of an estuary: (I) choose as many equally-spaced stations as practical; (2) estimate the varian ce of the mean (y) over bar by var (y) over bar=(1/10n(2))Sigma(j=2)(n ) (y(j)-y(j-1))(2), where y(1),..., y(n) are the measurements at the n stations; and (3) attain the desired precision by adjusting the numbe r of stations according to var (y) over bar proportional to 1/n(2). Th e inverse power of 2 in the last step is a consequence of the underlyi ng spatial correlation structure in San Francisco Bay; more studies of spatial structure at other estuaries are needed to determine the gene rality of this relationship. (C) 1997 Academic Press Limited.